ICL 7.3: Ocular Motor System

Question 1

Are oculomotor lesions localizing?

Answer 1

No!

The functions depend on a big circuit of structures and there could be problems in any of them and it’s hard to pinpoint where that is

Question 2

What are the 4 eye motor systems?

Answer 2

1. Saccades
2. Smooth pursuit
3. Vestíbulo-ocular
4. Vergence

Vestibulo-ocular system is the most important followed by vergence

Question 3

What is the major function of the saccades eye movement system?

Answer 3

These are quick eye movements that direct the fovea of the retina at the object of interest or new targets in the visual field (fovea is the center of the macula where you have the highest visual acuity)

In between the start and stop of the movement, there is no vision

Question 4

How is saccades initiated?

Answer 4

1. They can be initiated by auditory stimulus as well; it’s not just that you want to look at some object, it can be an auditory stimulus like if you hear a door open, you will use saccades to quickly look at the door to see who is coming in
2. It can be voluntarily initiated as well though; if you need to quickly skim a room to see everyone’s face for a fraction of a second just enough to identify who they are and then move on to find an empty chair to sit down
3. You can also use saccades from memory! If you work at a power plant and all the alerts are in the bottom left of the screen, because of memory any time you hear the noise you have to look to the bottom left immediately to address it

Question 5

What parts of the brain are used during saccades?

Answer 5

1. Cerebral cortex
2. Superior colliculus of the midbrain
3. Basal ganglia
4. Basal ganglia
5. Thalamus
6. Cerebellum
7. Para median reticular formation of the pons (acts as a network to connect different areas)

Slide 6 (not high yield)

Question 6

What part of the brain initiates saccades?

Answer 6

Frontal eye field

It’s contralateral though

So if you have a left frontal eye field tumor you will have difficulty initiating movement to the right

The left frontal eye field is going to try to push the eyes to the right and the right frontal eye field is going to try to push the eye to the left

So if you have a stroke or tumor or hemorrhage of the left frontal eye field, the right frontal eye field will push the eye to the left side TO THE SIDE OF THE LESION since it’s unopposed

Question 7

What is a hypermetric saccade?

Answer 7

When the patient overshoots their target that they’re trying to look at and then they have to re-center to make sure the object is on the fovea of the retina

So the motions are fast but the accuracy is abnormal so this is a cerebellum problem!

Hypometric = instead of overshooting, the eye undershoots and then has to keep going to get to the target

Question 8

What is the function of the smooth pursuit eye movement system?

Answer 8

The main function is to track a moving object smoothly

This is what you’re doing if you’re standing still and there’s something moving in front of you and your eyes are moving to track it like a bird flying around and you’re watching it fly around — or if you’re at a game and you’re following the motion of the ball

Because of the inherent delay in the visual system, this system needs to be predictive! So you have to predict which way the ball was moving, how fast it was going and where it’s going to be in the next fraction of the second so that your eye can be there when the ball gets there or how to find it if you lose the ball — so this requires a lot of calculation and it really complicated!

You can also use this system when you’re moving but the object is stationary — so you can use it to keep your eyes on a stationary object when you’re walking or running like during sports! Also older veterans will have great smooth pursuit because they’re trained to shoot a rifle at a moving target

This is also the same movement you use to read!!!!

Question 9

Which brain structures are involved in the smooth pursuit eye movement system? (This is not high yield)

Answer 9

1. Frontal eye fields
2. Dorsolateral pontine nuclei
3. Para median pontine reticular formation
4. Vestibular nuclei
5. Cerebellum
6. Striate cortex
7. Middle temporal and medial superior temporal areas

Just maybe recognize these but don’t remember them!

Question 10

What happens when there’s abnormal smooth pursuit?

Answer 10

The brain replaces the smooth pursuit with saccades!

There’s no smooth movement, it’s all just small jerky movements aka saccades!

Question 11

What is the function of the vestibulo-ocular eye movement system? (High yield!!)

Answer 11

The function is to optimize vision during head movements — you head is always moving so your vestíbulo-ocular system is always working even if you don’t realize it!

This system compensates for you head movements and makes your vision stable even though your head is moving all over so this is a super fast system!! It’s the fastest type of eye movement actually that a human can produce so it’s the only type of eye movement that is fast enough to compensate for head movements during walking, running etc.

Question 12

What is oscillopsia?

Answer 12

It’s like if you’re walking and it looks like you’re bobbing around; it gives you a headache

People will complain that their vision looks jerky, it’s bobbing up and down and they can’t stabilize it; it’s almost like a handheld video camera video that isn’t stabilized

So this is a problem with your vestíbulo-ocular system!

Question 13

What is the vestíbulo-ocular reflex?

Answer 13

It sort of counteracts the head movement

So if the patient turns their head to the left, the eye looks to the right to be able to stay focused on the same object — the eye moves as much in the opposite direction as the head did

Question 14

What parts of the brain are involved in the vestíbulo-ocular system?

Answer 14

The vestíbulo-ocular system spans the entire length of the brainstem so testing the VOR function is a great way to see if the brainstem is working well!

The cool thing is that if someone has congenital vestíbulo-ocular problems the cerebellum can try to compensate and people can do really well! So if one vestibular nerve is lost from a tumor or virus (acquired), therapy can help you learn to compensate and live a normal life

Question 15

What is the head thrust test?

Answer 15

It tests the vestíbulo-ocular system!

The doctor moves the patients head really quickly to the right and the patient is able to keep looking at the doctors nose; it looks like the eye isn’t moving

If the VOR wasn’t working normally, the eye would move with the head and then go back to look at the doctor

Question 16

What is nystagmus?

Answer 16

An involuntary to and fro eye movement with at least ONE slow phase

One slow phase and one phase phase = jerk nystagmus (more likely to be acquired)

Two slow phases = pendular nystagmus (more likely to be congenital)

Question 17

What is the function of the convergence eye movement system?

Answer 17

This is the type of movement you use to look at objects that are closer to your eyes

If you start looking at something close to your eyes there will be a mismatch, but then your brain will start the convergence process — so this system is used if the visual system notices an image mismatch between bilateral retina or if there is an image blur

This is also used during accommodations reaction/reflex

Question 18

What does normal convergence look like during a visual exam? What part of the brain is effected if this test isn’t normal?

Answer 18

The patient will be able to look at the cotton swab in the middle of their visual field as it moves closer to their nose

Their pupils will constrict and the eyes will move closer together as the swab moves closer!

So there is usually a midbrain problem if the patient isn’t able to do this!